In view of phasing out of leaded gasoline and restrictions on the aromatics content of gasoline fuels, there is a great impetus for developing processes which upgrade olefins to high octane components. One such class of materials is aliphatic tertiary ethers, such as methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME). However, the availability of isobutylene and isoamylene feedstock for these ethers is limited. Therefore, processes for making these olefins from readily available feedstocks are sought. The process described herein is one such process and involves the conversion of readily available refinery feedstock, such as olefinic gasoline, to products rich in lower olefins, such as isobutylene and isoamylenes.
The ability of shape selective zeolites such as ZSM-5 to convert olefins has been recognized previously. Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks, such as petroleum refinery streams rich in olefins, for the production of C.sub.4.sup.+ tertiary olefins. The C.sub.5 -C.sub.7 light naphtha range product of FCC operations is very rich in normal and branched mono-alkenes.
It has been discovered that a new crystalline material, designated MCM-41, is an effective catalyst for converting these intermediate olefins to propene and tertiary alkenes at high selectivity.